Pb(Zn.sub.1/3 Nb.sub.2/3)O.sub.3 (abbreviated as PZN) ceramic and Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 (abbreviated as PMN) ceramic are regarded as important raw materials in making of ceramic drivers and integrated layered capacitors mainly due to their high coefficients of electrostrictive and dielectric constants. However, only when PZN and PMN possess the structure of perovskite, then both of them possess the above properties and usefulness. Moreover, in the process of making these ceramics, it is very often that pyrochlore phase will occur which deteriorates these properties. Recently, the synthesis of PMN ceramic can be obtained by first pre-synthesizing the MgNb.sub.2 O.sub.6 phase and then reacting with PbO in order to form perovskite phase of PMN. While in the synthesis of PZN ceramic, even the ZnNb.sub.2 O.sub.6 phase is formed first, the perovskite phase cannot be fully obtained. As a result, common stabilizers such as SrTiO.sub.3, PbTiO.sub.3, BaTiO.sub.3, Ba(Zn.sub.1/3 Nb.sub.2/3)O.sub.3 or PbZrO.sub.3, etc. have to be added to facilitate the formation of PZN perovskite. The above additives can be used to stabilize the PZN perovskite but they may cause unfavorable influence on the inherent excellent properties of PZN. In light of the fact that the PMN perovskite ceramic possesses the properties similar to the PZN, it is advisable to synthesize the stable PMN perovskite first and then stabilize the PZN perovskite phase ceramic by employing the synthesized PMN as the additive, and form the Pb(Zn.sub.x Mg.sub.1-x).sub.1/3 Nb.sub.2/3 ]O.sub.3 perovskite phase ceramic raw materials. According to the preparation method of the present invention, no addition of additive as stabilizer is needed to effect the process. In conventional method of ceramics preparation with PZN as the basis, components such as PbO, ZnO, and Nb.sub.2 O.sub.5 are mixed together without the addition of perovskite phase stabilizer (such as SrTiO.sub.3, PbTiO.sub.3, BaTiO.sub.3), as a result, the perovskite phase PZN as indicated in FIG. 1 cannot be obtained. Consequently, the addition of a stabilizer is necessary. Furthermore, in the process of making the desired product with an appropriate ratio of PbO, ZnO, MgO and Nb.sub.2 O.sub.5, the amount of MgO should be greater than 35 mole %. By this process, about 80% of perovskite phase can be obtained. The properties of the obtained product has been illustrated in FIG. 4. It seems that the coefficient of dielectric constant does not exceed 13000.
Japanese Patent 57-25607 discloses a dielectric ceramic composition consisting 68.03-69.07wt % Pb.sub.3 O.sub.4, 2.43 to 3.98 wt % MgO, 0.15 to 3.15 wt % ZnO and 26.37 to 26.78 wt % Nb.sub.2 O.sub.5. Pb.sub.3 O.sub.4, MgO and Nb.sub.2 O.sub.5 are mixed and sintered at 850.degree. C. to produce Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3. Powered Pb.sub.3 O.sub.4, ZnO and Nb.sub.2 O.sub.5 were mixed and sintered at 850.degree. C. to produce Pb(Zn.sub.1/3 Nb.sub.2/3)O.sub.3. 75 parts wt of Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3, 25 part wt. of Pb(Zn.sub.1/3 Nd.sub.2/3)O.sub.3 and a vinyl acetate binder are mixed and compacted, and sintered at 1050.degree. C. for 1 hr. The sintered product has a dielectric constant of 14000 at 25.degree. C.